Method of Manufacturing a Polymer Jacketed Bullet

ABSTRACT

A method of producing a bullet with a polymer bullet jacket. The method of manufacture is accomplished by an injection operation that injects a molten plastic jacket around a suspended metal core in a simple and certain process.

CROSS REFERENCES TO RELATED APPLICATIONS

U.S. Provisional Application for Patent No. 62/016,353, filed Jun. 24,2014, with title “Polymer Jacketed Bullet and Method of Manufacturing”which is hereby incorporated by reference, Applicant claims prioritypursuant to 35 U.S.C. Par. 119(e)(i).

Statement as to rights to inventions made under federally sponsoredresearch and development

Not Applicable.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention related generally to bullets/projectiles (hereinafter referred to as bullets), and more particularly to a method ofmanufacturing polymer jacketed bullets.

2. Brief Description of Prior Art

It is well known in the industry to manufacture bullets andcorresponding cartridge cases of either brass or steel. Typically,industry design standards call for materials that are strong enough towithstand extreme operating pressures and which can be formed into acartridge case to hold the bullet, while simultaneously resist rupturingin the firing process.

Bullets are typically made of metal with hunting bullets being formed ofa lead body or core with or without jacketing by another metal as forexample, a copper jacket. Military ammunition will typically use steeljacketed bullets, which are erosive.

In all events, the friction between the bullets traveling through thebarrel and the barrel itself causes wear on the interior of the barrelwhich shortens its life and, at some point in time will begin tointerfere with the accuracy of the firearm. Furthermore, barrel foulingfrequently occurs from metal scraped from the surface of the bullet orthe jacket as a result of the friction. Prolonged firing of the firearmwithout cleaning can result in a loss of accuracy when the barrel isfouled.

A conventional bullet jacket is produced from gilding metal orcommercial bronze by deep drawing. A sheet of the metal is blanked,cupped, and annealed. After annealing, the cup is then pickled in acid,washed and drawn into the final form. The jacket is then trimmed priorto being filled with lead. Another technology used to produce jacketedbullets is electroplating, whereby a swagged lead bullet may be copperplated with an extremely heavy layer of copper. This process is slow andexpensive because the electroplating of individual parts is moredifficult to control.

It is also known in the art to coat a bullet jacket in a low frictionmaterial such as molybdenum disulfide, nylon, polyurethane orpolytetrafluoroethylene, for example. Such coatings however have beenapplied to the bullet jacket after the bullet is cast or swagged.

Regardless of the method used, in order for a bullet to achieve optimumterminal performance, its jacket and core must penetrate a target as asingle unit and remain connected throughout the course of travel,regardless of the resistance offered by the target material.

Therefore, there is a need for an improved method of manufacturing ajacketed bullet over the prior art that is simple and cost effective tomanufacture, and has sufficient durability to supplement or replace theconventional copper/zinc jacketing layer. The method of manufacture inthe present invention is accomplished by a less complex plasticinjection operation that injects a molten plastic jacket around asuspended metal core in a simple and certain process.

As will be seen from the subsequent description, the preferredembodiments of the present invention overcome disadvantages of the priorart. In this regard, the present invention discloses a process ofsuspending a projectile core in a plastic injection mold in order toinject a molten plastic jacket around the suspended metal core for thepurpose of replacing the commonly used copper/zinc alloys. Still otherobjects will become apparent from the more detailed description whichfollows.

SUMMARY OF THE INVENTION

In general, the present invention discloses a method of producing abullet with a polymer bullet jacket. The method of manufacture isaccomplished by an injection operation that injects a molten plasticjacket around a suspended metal core in a simple and certain process.

The core of the projectile is preferably made of a dense, malleablymaterial, such as lead or a lead alloy, however the core could also bemade of a non-lead material, malleable metal.

In manufacture, the core of the projectile is positioned within the moldsuch that the core is suspended within the cavity of the mold so thatthe surface of the core is not in contact with the interior surface ofthe mold. The positioning of the core may further be aided with at leastone alignment pin.

After the core has been properly aligned, a thermal-plastic material isinjected into the cavity via injection port. The injected material mayentirely encapsulate the core, or alternatively, need only cover aportion of the core.

During the injection process, it is important to ensure that bondingincurs between the core and the injected material. One way to insurethat adequate bonding is achieved is to heat the plastic material as hotas the material characteristics will allow, and to inject the materialas quickly as possible. This allows the core to be heated by, andthereafter bonded to, the injected material.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded view of a preferred embodiment of the presentinvention, a method of manufacturing a polymer jacketed bullet.

FIG. 2 is a side view of the method of FIG. 1, with the core of aprojectile in broken lines.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention is directed to polymer jacketed bullets, andmethod of manufacturing the same. The preferred method of manufactureincorporates a plastic injection operation that injects a molten plasticjacket around a suspended metal core that eliminates a number of thesteps required in the prior art. The present application furtherdiscloses a projectile having a metal core surrounded by a plasticjacket made from a flexible, resilient material that will reducefriction between the bullet traveling through the barrel and the barrelitself. As will be described, the polymer jacketed bullet and method ofmanufacturing as disclosed further consists of components configured andcorrelated with respect to each other so as to attain the desiredobjective.

As is known, the core of the projectile is preferably made of a dense,malleably material, such as lead or a lead alloy, however in the presentinvention, the core could also be made of a non-lead material, such asbismuth, bismuth alloys, tungsten, tungsten alloys, tin or tin alloys,or any other dense, malleable metal that as will be described, will bondto the jacket. The bullets of the present invention are manufactured byan injection molding process from a composite polymer by feeding thepolymer through an injection molding apparatus. The properties of theselected polymer material provide several advantages over theconventional brass and lead materials commonly used for cartridge casesand bullets, respectively. For example, the polymer material provides away for the jacket to hold the bullet that replaces the prior art stepof crimping and eliminates a need to use adhesives in cases whereadhesives are required to provide the proper bullet pull properties whenusing brass cases. Further, brass cartridge cases tend to form to thechamber was of the firearm when fired. In contrast, the compositepolymer jacket of the present invention flexes during firing, but thematerial memory returns the jacket to its original dimensions.

In application, the core 12 of the projectile is positioned within acavity 15 of a mold 20. Referring to FIG. 2, as shown, the core 12 ispositioned in the cavity 15, the core 12 shown in broken lines. In thisposition, the core 12 is suspended within the cavity 15 so that theouter surface 12 a of the core 12 is not in contact with the interiorwas 21 of the cavity 15, such that a spacing 17 is disposed between theouter surface 12 a and the interior walls 21. The positioning of thecore 12 may further be aided with at least one alignment pin 16 of themold as illustrated in FIG. 2.

After the core 12 has been properly aligned within the bottom portion 22of the mold 20, the top portion 23 is aligned with the bottom portion22. When the bottom and top portions of the mold 20 fixture have beenaligned, a press may be utilized to maintain the alignment during thehigh-pressure injection procedure.

A thermal-plastic material (not shown) is heated to at least the meltingtemperature, or preferably slightly above the melting temperature of thematerial, and is injected into cavity 15 via injection port 30. Asillustrated, the core 12 has a front end 13 and a body 14. The injectedmaterial may entirely encapsulate the core 12, or alternatively, needonly cover a portion of the core, preferably the body portion 14.

During the injection process, it is important to ensure that bondingincurs between the core 12 and the injected material, One way to insurethat adequate bonding is achieved is to heat the plastic material as hotas the material characteristics will allow, and to inject the materialas quickly as possible. This allows the core 12 to be heated by, andthereafter bonded to, the injected material.

It should be understood with the present process, the jacket of theprojectile is now made from a flexible, resilient material such aspolytetrafluoroethylene so that the jacket takes most or essentially allof the deformation of the projectile and barrel when the projectile isfired. The jacket of the projectile thus protects the lead or ceramiccore from deformation or damage and reduces wear on the barrel. Inaddition, when the projectile leaves the barrel, the ridges on theprojectile formed by the rifling grooves of the barrel either reduce insize or disappear altogether. The projectile consequently has asmoother, more aerodynamically efficient surface during flight and has amore accurately predictable flight path.

It should be further understood the present invention is not limited toa particular-described caliber and is intended to be applicable to othercalibers as well.

Several benefits therefore occur as a result of using bullets coatedaccording to the invention. For one, there is a dramatic reduction inbarrel fouling from surface metal of the bullets, particularly surfacemetal from the jackets of bullets. The clearly reduced friction duringbullet travel through the barrel reduces wear on the barrel and therebylengthens the useful life of the barrel.

Because of the increased slipperiness of the bullets due to the reducedfriction, peak pressures present in the barrel during the firing of thefirearm are reduced which in turn allows a given firearm to firecartridges loaded to achieve higher velocities, all the whilemaintaining safe pressures.

Bullets made according to the method of the present invention may befired with enhanced accuracy as a result of reduced variances infriction during firing. It also appears that the reduction in frictionserves to dampen vibration of the barrel as the bullet travels throughit, further enhancing accuracy.

Because of the lack of fouling, the firearms do not require cleaning asfrequently.

It is expected that there will be an improvement in long rangeballistics as a result of smoother airflow about the bullet due to theimproved lubricity of its surface.

It is also expected that there will be improved penetration into atarget, particularly when using hunting bullets, due to the increaselubricity of the bullet surface.

In repeating firearms, particularly semi-automatic firearms, improvedreliability in feeding and chambering is to be expected again, due tothe high lubricity of the surface of the bullet. It is expected thatthere will be a lesser loss of accuracy for sustained firing of afirearm due to slower temperature rise of the barrel. In particular,because there will be less friction using bullets made according to thepresent invention, less heat due to friction will be generated and thetemperature rise rate of the barrel will be slower.

Lastly, but certainly not least, the manufacturing process as describedherein, is cost effective in both labor hours and material. Asdisclosed, plastic material is replacing the more costly copper and zinccommonly used for making bullet jackets in the prior art. Further, anumber of steps required in the prior art manufacturing process are noweliminated. It will therefore be appreciated that bullets made accordingto the invention and method of invention possess substantial advantagesover those heretofore known.

Although the above description contains many specificities, these shouldnot be construed as limiting the scope of the invention but as merelyproviding illustrations of some of the presently preferred embodimentsof this invention. As such, it is to be understood that the presentinvention is not limited to the embodiments described above, butencompasses any and all embodiments within the scope of the claims.

It will be obvious to those skilled in the art that modifications may bemade to the embodiments described above without departing from the scopeof the present invention. Thus the scope of the invention should bedetermined by the appended claims in the formal application and theirlegal equivalents, rather than by the examples given.

1. A method of manufacturing a bullet comprising the steps of: positioning a core within a cavity of a mold such that the core is suspended within said cavity so that the entire outer periphery of the core is not in contact with an interior surface of said cavity, supporting said core within said cavity with at least one alignment pin, injecting a thermoplastic material into said cavity via an injection port such that the injected material covers a portion of the core.
 2. The method as recited in claim 1, including the step of heating the thermoplastic material above a melting temperature of the thermoplastic material, and then performing the injecting step as quickly as possible.
 3. The method as recited in claim 2, wherein in the injecting step, the injected material only covers a body portion of the core.
 4. The method as recited in claim 3, wherein in the injecting step, the injected material does not cover a front end of the core.
 5. A method of manufacturing a bullet comprising the steps of positioning a core within a cavity of a mold such that a spacing is disposed between an entire outer periphery of an outer surface of said core and an interior wall of said cavity; and injecting a thermoplastic material into said cavity such that said injected material covers a body portion of said core, and wherein a front end portion of said core is not covered with said injected material.
 6. The method of claim 5, wherein said core is positioned in said cavity using at least one alignment pin. 